The present invention relates generally to rotating electrical machines and, more particularly, to a brush holder for a rotating electrical machine.
Electrical machines such as motors, generators, and alternators commonly use brushes made of an electrically conductive material such as carbon to provide electrical power to the rotor of the machine. Typically, two brushes are provided, one as input power and the other as a return path. A brush holder maintains the position of the brushes with respect to the slip rings on the rotor.
Because the brushes are made of carbon, brushes are subject to wear. Once the brushes wear, they must be replaced. To increase the brush wear, the position of the brush should be maintained in a perpendicular orientation to the slip ring.
Known brush holders, however, are commonly molded of a plastic material. In these brush holders, the brush holder cavity is tightly formed around the brush. However, the molding process restricts the tight tolerances. The brush holder cavities are formed with drafted surfaces that are canted slightly from true 90xc2x0 angles. This allows the mold to be more easily removed. As the brush begins to wear and the end of the brush begins to move further toward the rotor, the brush may move laterally due to the drafted surfaces and therefore not maintain its perpendicular orientation to the slip rings. This allows premature brush wear.
It would therefore be desirable to provide a brush holder that allows the position of the brush to be maintained throughout the life of the brush.
It is therefore one object to provide a brush holder for a rotating electrical machine that provides increased brush wear by maintaining the brush in a substantially perpendicular orientation to the slip ring.
In one aspect of the invention, a brush holder assembly for rotating electrical machine having a brush comprises a brush holder housing having an elongated cavity therein. The cavity is defined by a first wall, a second wall, a third wall, and a fourth wall. The cavity is sized to receive the brush. The brush cavity has a longitudinal axis that corresponds to the direction of movement of the brush. At least one of the first wall, the second wall, the third wall, and the fourth wall comprise a first drafted surface. A first rib is positioned on the drafted surface. The rib is substantially parallel to the longitudinal axis.
In a further aspect of the invention, the longitudinal axis is perpendicular to the slip ring of the rotor of the rotating electrical machine. One advantage of the invention is that the brush holder ay be easily molded while the ribs maintain the rush in the desired orientation.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.